1. Field of the Invention
This invention generally relates to regenerative cells derived from a wide variety of tissues, and more particularly, to adipose-derived regenerative cells (e.g., stem and/or progenitor cells), methods of using adipose-derived regenerative cells, compositions containing adipose-derived regenerative cells, and systems for preparing and using adipose-derived regenerative cells which are used to promote wound healing, e.g., wounds resulting from diabetes, chronic peripheral vascular disease and obesity.
2. Description of Related Art
Approximately five million Americans suffer from chronic open sores often due to limited blood flow which can slow the body's own healing process. Normally, injury to the skin sets into motion a complex cascade of events which ultimately results in wound healing, namely the formation of the neodermis and re-epithelialization. This complex sequence of events includes a symphony of interaction between local, regional and systemic growth factors, cytokines, as well as cellular participants, including mesenchymal stem cells. Inadequate and/or incomplete wound healing, however, can lead to significant individual morbidity including a profound reduction in quality of life. Sores can become seriously infected, gangrenous and in some cases require amputation. For example, the primary cause of non-traumatic amputation due to inadequate wound healing is diabetes. There are nearly 16 million diabetics in the United States. More than 67,000 patients with diabetes require surgical amputation each year, necessitating long and costly rehabilitation. For many, mobility and independence are severely affected, permanently altering their quality of life. At its extreme, poor wound healing can serve as the root cause of death.
For patients who have chronic wounds that are difficult to heal, basic medical and surgical care is essential, but not always enough. Current therapies for wound healing include removal of unhealthy tissue, use of growth factors, hyperbaric (high-pressure) oxygen treatment, advanced wound dressings, antibiotic therapy, conventional wound dressings, nutrition counseling, education/prevention, surgery, and physical therapy. For example, manipulation of a single or a combination of participating molecules, including but not limited to PDGF-BB and bFGF, can be used to augment natural wound healing. In addition, application of “engineered” cellular products (Apligraf® and Dermagraft®) as a way of engendering a more physiologic pattern of growth factor expression can also been used. The implementation of therapies like Regranex, a platelet-derived growth factor which stimulates healing, has also proven to be beneficial for wound care in appropriate patients.
The regenerative cellular approach has also enjoyed relative success compared to single or combination molecular therapies described above. Regenerative medicine harnesses, in a clinically targeted manner, the ability of stem cells (i.e., the unspecialized master cells of the body) to renew themselves indefinitely and develop into mature specialized cells. Broad application of regenerative cellular therapy, however, has been hindered by questions of cellular retention and the high costs associated with extensive ex vivo manipulation. However, although stem cell populations have been shown to be present in one or more of bone marrow, skin, muscle, liver and brain (Jiang et al., 2002b; Alison, 1998; Crosby and Strain, 2001), their frequency in these tissues is low. For example, mesenchymal stem cell frequency in bone marrow is estimated at between 1 in 100,000 and 1 in 1,000,000 nucleated cells (D'Ippolito et al., 1999; Banfi et al., 2001; Falla et al., 1993). Similarly, extraction of ASCs from skin involves a complicated series of cell culture steps over several weeks (Toma et al., 2001) and clinical application of skeletal muscle-derived stem cells requires a two to three week culture phase (Hagege et al., 2003). Thus, any proposed clinical application of stem cells from such tissues requires increasing cell number, purity, and maturity by processes of cell purification and cell culture.
Although cell culture steps may provide increased cell number, purity, and maturity, they do so at a cost. This cost can include one or more of the following technical difficulties: loss of cell function due to cell aging, loss of potentially useful non-stem cell populations, delays in potential application of cells to patients, increased monetary cost, and increased risk of contamination of cells with environmental microorganisms during culture. Recent studies examining the therapeutic effects of bone-marrow derived ASCs have used essentially whole marrow to circumvent the problems associated with cell culturing (Horwitz et al., 2001; Orlic et al., 2001; Stamm et al., 2003; Strauer et al., 2002). The clinical benefits, however, have been suboptimal, an outcome almost certainly related to the limited ASC dose and purity inherently available in bone marrow.
Recently, adipose tissue has been shown to be a source of stem cells (Zuk et al., 2001; Zuk et al., 2002). Adipose tissue (unlike marrow, skin, muscle, liver and brain) is comparably easy to harvest in relatively large amounts with low morbidity (Commons et al., 2001; Katz et al., 2001b). Suitable methods for harvesting adipose derived stem cells, however, are lacking in the art. The existing methods suffer from a number of shortcomings. For example, the existing methods lack partial or full automation, a partial or completely closed system, disposability of components, etc.
Given the therapeutic potential of adipose derived stem cells for wound healing, there exists a need in the art for a method for harvesting cells from adipose tissue that produces a population of adult stem cells with increased yield, consistency and/or purity and does so rapidly and reliably with a diminished or non-existent need for post-extraction manipulation.